The ozone layer depletion (OLD) in the stratosphere is a rather old theme which was found early 1970s. A large loss of total ozone as ozone hole in Antarctica pole was found by Farman et al. in 1985 [1]. This observation triggered international effort to prevent the ozone layer from further depletion. Scientists starting from F. Sherwood Roland and Mario Molina (Novel prized later 1996) successfully established a mechanism of ozone layer depletion chemistry [2]. This situation led the Montreal Protocol in 1987 and its revisions in 1990 (London), 1991 (Nairobi), 1992 (Copenhagen), 1993 (Bangkok), 1995 (Vienna), 1997 (Montreal), 1997 (Kyoto), and 1999 (Beijing). Twenty four nations including the U.S. signed an agreement to freeze the production five different CFCs 1986 levels and to cut the production in half of 1986 level by 1999. A list of ozone depleting substances (ODS) is available, along with their ozone depletion potential (ODP), global warming potentials (GWP) and CAS numbers. (www.epa.gov/science/ozone/ods.html).
Ozone depletion trend amazingly was reported to have got flat since 1995 [3] while National Oceanic and Atmospheric Administration (NOAA) report of Oct. 21, 2011 said ozone hole level in the atmosphere above the South Pole dropped to seasonal low of 102 Dobson Unit October 9 to be the 10th lowest point in the 26 years record. Sep. 29, 2013 season high 116 Dobson unit was observed showing improvement but still long way to recover to the level of normal Dobson unit 350 and above. Updated The Antartic ozone hole and where we are now with stratospheric ozone depletion syndrome was reported by Douglass et al. [4]. Laube et al [5] analyzed the firn snow in Greenland and found that CF3CCl3 and CF3CH2Cl continued to increase instead of decrease in the period of 1990s-2012 while CFCl2CFCl2 and CF2 ClCCl3 decreased slowly. The source of CF3CCl3 and CF3CH2Cl needs to be investigated.
Based on observed variation of chloride decline rate of year to year fluctuation, Strahan et al. [6] predicted the ozone hall shrink will be achieved by 2040. Ozone Depletion free Freon gases such as HCFCs or HFCs were reported to have Ozone Depletion Potential index (ODPI)≦0.002 compared to 1.00 of related ODPI of CFC-11 (CCl3F) [7].
The ionization conditions of IMS and APIMS reaction region and the environment of stratosphere appear to be similar. As a result, studies of electron—molecule reactions that occur in the stratosphere can be simulated with the IMS or APIMS in the laboratory conditions. Simulation test results for the ozone layer depletion occurring in the stratosphere may bring a clearer picture of ozone depletion chemistry in the stratosphere.
Halide Compounds are easily Detected by Electron Capture Detector (ECD). In 1972, J. E. Loblock, who invented ECD for Gas Chromatography (GC), detected CFC-11(CCl3F) with collaborators in the atmosphere using his ECD-GC [8]. A series of Freon gases including CFC-113 (C2 F3 Cl3) eluted by FID-GC and were identified by both positive and negative product ions by Plasma chromatograph (PC) (early name of IMS) [9]. The reduced ion mobility, K0, of Cl−, Br−, and I− reported appear to be 2.97±0.02, 2.63±0.02, and 2.53±0.02 cm2·v−1·s−1 respectively [10,11]. Halide ions were reported with even higher sensitivity were detected with slight amount oxygen doping [12,13] by Atmospheric Pressure Ionization Mass Spectrometry (APIMS).
Although a breakthrough technique of field asymmetry ion mobility (FAIMS) or diffusion mobility spectrometry (DMS) [14-16], which is featured in identification of isomers, isobars, and conformers for the compounds of biologically active molecules, pharmaceuticals, and biomedical compounds, is available and making remarkable progress. Our work however will be done with well established hardware of classic standard IMS-Ni-63. Based on the data from the physical parameter studies [17, 18] to improve the peak to peak resolution and total ion current, the hard ware size evolution was significantly improved and reduced to have total tube Length×Width×Height=13 cm×4 cm×4 cm from a large laboratory scale of original research type instrument of PCP Corporation [19] and believed to be one of the optimal configurations widely used in the IMS/MS system now.
Updated Chemistry of Ozone Depletion. Ozone Layer or Ozonosphere is a layer in the atmosphere which stretches from roughly 10-50 km (or 7-30 miles) above the Earth's surface. It is in between troposphere and stratosphere. Ozone Layer is believed to be formed primarily from interaction between oxygen in its three different forms of O2, O, and O3. i.e. O2 uvc--->2O; O+M+O2--->O3+M as an exothermic reaction −105 kJ/mol or −25.12 kcal/mol. The updated OLD chemistry was well established [2,20]. That is the CFCs such as CF2CL2 (Freon 12) and CFCL3 (Freon 11) dissociate to release one odd electron Cl. atom as a free radical by the UV radiation from the Sun. i.e.
Reactions 1,2, and 3 representing how ozone is destroyed producing two odd electron species that is one Cl. atom and one free radical ClO. Reaction 3 may be slower than reaction (2) because it will be dependent upon the concentration of oxygen atom which is less than O3. However ClO. formed thus reacts with atomic state of Oxygen to reproduce Cl. in Reaction 3. This Cl. atom like a catalyst repeatedly is believed to be involved in O3 depletion. Likewise Br, I, NO, OH, undergo O3 depletion reaction by BrO, IO, NO2, and HO2 respectively. Using Eddy diffusion coefficients modeled vertical turbulent motion, calculated life time of CFCs is reported to fall 40-75-140 years [2]. At stratospheric temperature, ClO. reaction with O is reported to be six times faster than the reaction of NO and NO2 with O. As a result, Cl—ClO chain is known to be more effective than the NO—NO2 chain in the catalytic conversion in the Reaction 2 and 3 [2,20].
The estimated photo dissociation rates of CFCl3 and CF2Cl2 at the altitude of 30 km are reported to be 3×10−7 cm3 molecle−1s−1 and 3×10−8 cm−3 molecule−1 s−1 respectively. The peak rate destruction and formation of Cl. occurs at 25-35 km altitudes where the concentration of O3 is high. The troublesome odd electron chain such as OH, HO2; NO, NO2; Cl, ClO can only be terminated by interaction with one another or others to convert to even electron species. Possible termination involving the Cl series with itself Cl.+ClO.--->Cl2O or with one of others i.e. Cl+NO--->NOCl temporarily terminated. However if photolysis takes place, both chains involves in ClO+NO--->Cl+NO2 rather in slow rate. The ClO reaction with NO2 will be rapid:ClO.+NO2---->ClONO2  (4)C1.+CH4---->HCl+CCH3  (5)Reaction 4 is rapid and 5 is slow but significant reaction to terminate the catalytic chain cycle for Cl. atom. HCl can be formed by reaction 5 in the temporary termination of Cl. atom chain. Whether or not the restarting reaction of OH+HCl--->H2O+Cl. depends primarily on concentration of OH. Photolysis of CFCs including CFCl3 and CF2Cl2 does not occur in troposphere because these molecules are transparent to UV wave length higher range than 290 nm [2]. These mechanisms however were established under the assumption of no free electrons exist in stratosphere.
Electrons in stratosphere. However among solar energetic particles electrons out of Belt radiation so called Relativistic Electrons Precipitation (REP) penetrate deep down to stratosphere [21-22]. The REP can provide a local source of upper stratospheric nitric oxide (NO) which can be formed through between electrons and neutral air at the stratosphere. This nitric oxide plays a major role in the removal of stratosphere ozone as discussed above [23].
Using stratospheric balloon soundings, production of electrons with high energy were observed in stratosphere at latitude 23° South, Longitude 47° West by Van et al [24]. Using a Proton/Electron Telescope (PET), SAMPEX, a comprehensive measurement of energetic electrons was made in 1993 by Cook et al [25]. Multi level, 1-15 Mev, electrons deeply penetrate into atmosphere to be source of ionization in the middle altitude regions.
Since the role of halide compounds in destruction of the stratospheric ozone was discovered, HCFCs (hydrochlorofluorocarbones) have been in use in many applications in place of CFCs. Even though the short life time to reach stratosphere and calculated very low level of ODPI values of HCFCs were reported to be very low [7], sooner or later though HCFCs might be a dominant source of Cl. in stratosphere. As reported by Hossaini [26], the short lived (six months) halogens that is originated from primarily anthrophgenic appear to deplete ozone in the rate half of the CFCs. This HCFCs are not controlled by the Montral Protocol. Short lived HBrFCs was reported to have 3.6 times higher than that of HCFCs. This issue was reported to be discussed at the Montreal Protocol meeting, April 2015, in Bankock on the substances that deplete the ozone layer [27]. Cicman et al [28] in their electron/molecule beam study, found the energy (0-8.6 eV range) needed for associative or dissociative electron attachment at gas temperature 300° K. Four fragment negative ions of Cl−, F−, CClF−, and CF2− were observed. This is similar energy range to the electron energy level emanating from the Ni-63 isotope of IMS and APIMS ionization source at ambient temperature. Thus depending on the electron density flux, electrons are involved in e-ion-molecule reactions with halides in the stratosphere.
If electrons are available in stratosphere, one expects the interaction between electrons and chemicals such as CFCs, HCFCs, NOx, COx, H2O, and other air constituents in that environment. In an effort to see interaction between electrons and Cl., electrons were intentionally shot up to stratosphere 40 km high altitude and treated data by computer simulation. The electron capture by Cl. to react with O3 i.e. Cl−+O3--->ClO−+O2. This reaction is believed not to be as favorable as the reaction (2) due to the EA of Cl>EA of ClO. Boosting electron affinity (EA) by hydrated Cl−, (H2O)Cl−, to 4.6 eV level from 3.6 eV the reaction type of (2) is even harder [29]. (See Table 1). As a result, we prevent the Cl. from being a catalyst in the reaction (2). Relativistic electron flux at 50 km high altitude was reported to be 800/cm3 [30].
TABLE 1Electron Affinities of Related Molecules [31]MoleculesElectron Affinity (EA eV)NO33.073Cl3.611F3.399Br3.364CO33.260I3.059I22.520Br22.420Cl22.400IO2.378BrO2.353ClO2.278NO22.270O32.103OH1.829O1.462O20.452
Lu et al [32] reported that the absolute cross sections for dissociative capture of 0 eV electrons to CFCs and HCFCs are strongly enhanced by presence of H2O ice polar stratospheric cloud. The absolute cross sections for CFCl3, CHF2Cl, and CH3CF2Cl were reported to be 8.9×10−14, 5.1×10−15 and 4.9×10−15 cm2 at 0 eV respectively. The value for CFCl3 and CHF2Cl are 1 order of magnitude higher than that in gas phase, while the CH3CF2Cl is 3-4 magnitude higher. The cross section enhancement is interpreted to be due to electron transfer from precursor states of solvated electron in ice to an unfilled molecular orbital of CFCs or HCFCs followed by dissociation. This study indicates that electron induced dissociation on ice is a significant process that lead Cl− formation after breakup. As a finishing result, this means that the activity is expected to occur slowly than predicted in the O3 destruction process.
In FIG. 1, the ion chemistry of the low atmosphere from the mesosphere to the stratosphere, and the troposphere were summarized [Ref. 33]. In the stratosphere, O3+e-->O3− is formed first. By the third body M (O2) subsequently releases O− e.g. O3−+O2+M--->O−+2O2, the dissociated oxygen ion, O−, is formed. This atomic state oxygen combine with other oxygen molecule to form O3−: that is O−+O2--->O3−. In the upper part of stratosphere as the concentration of CO2, NOx, and SOx gas increase, O− ion reacts with these molecules to form CO3−. NO3−, and SO3− respectively. While the ion chemistries of the lower part of stratosphere and the troposphere progress further into complex terminal particles.
Prior to the time of the ozone destruction reaction mechanism [2] with the above reactions (1-3) were proposed, mass spectrometers were launched into stratosphere using a balloon or rocket platform [34-37]. When negative ions were drawn into a quadrupole mass spectrometer through sampling orifice, O−, NO2−, and Cl− (contaminant ? or from CFCs?) were observed at the altitude above 78 km (mesosphere), and CO3−, HCO3−, NO3−, and Cl− were observed below 78 km. In the mesosphere. When negative ions were again drawn into a quadrupole MS through sampling orifice, OH−, (H2O)CN−, (H2O)NO2−, (HOCl)NO2−, (HCN)NO3−, (HCl)NO3−, (HOCl)NO2−, (H2O)(HNO3)NO3−, (HOCl)NO2−, (H2O)(HNO3)NO3−, (HOCl)HSO4−, (HNO3)(HNO2)NO3−(H2O)(HNO3)HSO4−, (H2O)(HNO3)2NO3−, and (H2O)(HNO3)(H2SO4)HSO4− were observed at 32 to 35 km, and core ions of NO3− were observed at 20 to 28 km in the stratosphere. These results coincides with the conclusion of ion chemistry upper atmosphere reported by Smith et al. [33] (see FIG. 1). These results clearly describe that the reaction O3− with CO2 to produce CO3− with NO2 subsequent reactions producing NO3−. The significance of increasing greenhouse gas CO2 and NO3− effect to ozone depletion cannot be ignored in this regard.
Ozone Measurement Instruments
Since early 1920s the study of ozone concentration in atmosphere instruments have been evolved from ground based spectrometers to balloons, aircraft, rockets, and satellites. These developments have enabled measurements to expand from the atmosphere of isolated ground station to daily global coverage and profiles of ozone in the atmosphere.
Groudbased Measurement. Since 1924, Dobson Spectrometer (Dobsonmeter) by Gordon Dobson [38] and Brewer Spectrophotometer, known as Mark III [39] have been in use as ground based measurement instruments. It measures the total ozone by measuring the relative intensity of the dangerous UVB (305 nm) radiation to the UVA (325 nm) radiation absorbed by the ozone layer using Umkehr method to deduce vertical distribution. However drawbacks are that it is strongly affected by aerosols and pollutants in the atmosphere because they absorb the UV light at the same wave length region. Measurement is usually localized small area. LIDAR [40]. A telescope is used to collect UV light that is scattered by two laser beams one of which is absorbed by ozone (308 nm) and the other is not (351 nm). By comparing the intensity light scattered from each laser, a profile of ozone concentration vs. altitude is measured from 10 to 50 km.
Airborne Measurement. Airborne measurements of ozone provide a direct in situ method of determining ozone concentrations in the atmosphere. Balloons, Rockets, and Aircraft carry instruments into the atmosphere to measure accurate ozone concentration. However, the measurements are made only localized regions and can't provide a global picture of ozone distribution. Balloons [26, 41]. Balloons have been used almost as long as ground devices to measure ozone. They can measure the change in ozone concentration with altitude as high as 25 miles (40 km) and provide several days of continuous coverage and many devises used to measure ozone from balloons so called Ozonesondes. Several instruments can be carried at once and simultaneous measurements of many parameters can be conducted. However since balloons are unpowered flight path cannot be controlled.
Rockets. Rockets measure profiles of ozone levels from the ground to an altitude of 75 km by using photo spectroscopy. Rockets provide all weather capability but are limited by their short life and narrow coverage in geographic range [41].
Aircrafts. Airplanes are used to make detailed measurements of ozone levels and related chemicals in the troposphere and lower atmosphere. Typical missions include 10 or more instruments capable of measuring ozone, chemicals related to the production and destruction of ozone, and atmospheric conditions that affect ozone. In 1987, the Airborne Antarctic Experiment determined that the ozone hole over Antarctica was caused by anthropogenic chlorine. However measurements from aircraft are restricted by concerns for pilot safety, range, and flight duration, and are not continuous [41].
Satellites. Satellites measure over the entire globe every day providing comprehensive data. In orbit, satellites are capable of observing the atmosphere in all types of weather, and over the most remote region on Earth. They are capable of measuring total O3 levels for mapping, profiles, and elements of atmospheric chemistry. Various spectrometers of TOMS (Total Ozone Measurement Spectrometers) were used during 1994-1997 and OMI (Ozone Measurement Instrument) took over the TOMS's roll [39]. Summary of ground level based TOMS and trend of ozone profile measurement was reported [4,42].
Aurora Program. www.esa.int/SPEClALS/Aurora/MZOS39ZAD_0.html, [41]. In 2001, Eropean Space Agency (ESA) was established as a space flight program with first objective of Solar system exploration using robotic spacecraft and human spaceflight. Secondary objective is to search for the life beyond the Earth. This program is a system equipped with four different spectroscopic instruments which are a Infra Red High Resolution Dynamics Limb Sounder (HIRDLS), a microwave emission spectroscopy named Microwave Limb Sounder (MLS), Ozone Monitoring Instrument (OMI) as mentioned above, and a Fourier Transfer Infra Red Spectrometer, named Tropospheric Emission Spectrometer (TES). The technique involved by far is based on the UV-IR absorption or emission spectroscopy [43].
Ion Mobility Spectrometry (IMS)
IMS appears to be another available technique capable to detect O3 and other related gases such as NO, NO2, NO3, H2O, NH3, and SO2, including CFCs, BrFCs, IFCs, HFCs, and HCFCs in the atmosphere with very high sensitivity. The IMS is a technique closely aligned to mass spectrometry which operates at atmospheric pressure conditions [44-49]. It chemically ionizes sample drawn into the reactor with sets of reactant ions (established for by selecting dopant gas or gas phase chemicals), and separates the un-reacted reactant and reacted product ions through a drift tube for detection under atmospheric conditions. The process whereby ions are separated in the drift region is known as mobility. Since mobility depends on collisions of ions with drift gas, it depends also on density as well. Thus the correction of the mobility to standard conditions (K0) will be:Reduced Mobility (K0)=K×P/760×273/T  (6)Or (K0)=L/dt.E×P/760×273/T  (7)where L is drift length, dt drift time, E field gradient, P ambient pressure in Torr or mmHg, and T is temperature (273 K.°). Equation (7) is normally used for routine laboratory work.
IMS is an ionization technique, however due to the interference of COx and NOx, it suffers the same difficulties in detecting ozone as the mass spectrometer technique does as described above [33-36]. For this reason, the Global Merit Development is taking a different approach. First it has assembled a reaction sphere in which the neutral reactions thought to deplete ozone can be simulated. Secondly in order to remove the interference of COx and NOx, etc, ammonium hydroxide vapor, is introduced into carrier gas inlet system of the reaction sphere as a dopant chemical. By introducing the products of those reactions into the IMS the product ions are detected and identified.
Currently remarkable progress in ultra miniaturization with the technique of FAIMS has been reported [14-16]. Electro Spray Ionization (ESI) technique for mass spectrometry invented in 1989 [50,51] provided an opportunity to analyze large bio molecules by the IMS/MS system for the isomers in particular. The handicap of FAIMS is unable to provide reduced mobility value which is vitally important for identification purpose by the IMS only. A comprehensive review was made on the “IMS as a technique rediscovered for head space vapor site analysis” by Eiceman [52]. Negative ion mode of IMS addresses the same issues as the Electron Capture detector (ECD) together with an additional capability to monitor both negative and positive product ion spectra similar to the APIMS by which the sample molecules can be identified [53].
Significant miniaturization work was achieved by the Bendix corporation (former organization of Smith Detectors) in the period of 1977-1980s [18]. Reasonable trades were made between performance requirement such as sensitivity, selectivity, resolution power, response time, reliability, and repair maintainability for the application. The result was a microprocessor based IMS system which could be operated independent of ancillary gas supplies with selectable specificity. This type of hardware with various chemistries is available from Smiths Detection (USA&UK) and information on similar hardware was reported on [52].
The types of ion/molecule reactions occurring in the reaction region in the IMS can be summarized as follows:
Positive Ion ModeNegative Ion ModeProton TransferElectron Capture (associative)RH+ + M → MH+ + Re− + M → M−Ion AttachmentDissociative Electron CaptureR+ + M → MR+R− (e) + MX → X− + RCharge TransferCharge TransferR+ + M → M+ + RR− + M → M− + RProton AbstractionR− + MH → RH + M−Ion AttachmentR− + M → MR−
Proton transfer reaction: this reaction is accomplished by allowing the protonated trace water reactant ions, i.e. (H2O)nH+, to react with the gas phase sample molecules M if the sample molecule has higher Proton Affinity (PA) depending on the sample concentration and relative PA. The PAs of water, acetone, ammonia, and (acetone)2 appear to be 168.9, 193.6, 200.7, and 225.6 kcal/mole. All types of freon gases including CFCs did responded in the positive ion mode with very possibly as MH+ ions in early by PC (IMS) study [8]. Reaction mechanisms for positive ion mode are well described in references of [43-48].
Associative electron capture reaction in the Negative Ion Mode: in the reactor environment of Ni-63/IMS thermal electron, having average energy of 0.5 eV, is captured by sample molecule M to be M−, if the sample molecule has electron affinity (EA) is >0.5 eV. Compounds having slightly higher than 0.5 eV or equal undergo the associative electron capture or resonance capture [31,53]. Ozone molecule having EA 2.103 eV would undergo an associative electron capture reaction in the IMS reactor i.e. O3+e→O3−. The Cl. radical formed by the UV irradiation, would undergo interaction with O3− i.e. Cl.+O3−→O2+ClO−. Unlike neutral radical, the charged ClO− energetically is un stable and Cl− ion takes charge to release the Atomic state O and the Cl− eventually sink down by forming (H2O)n HCl. The same is for (H2O)nCO4.
Dissociative electron capture: when EA of the sample is considerably higher than the thermal level, the sample molecule capture electron first and subsequently undergo dissociation reaction [53]. For instance the CFC-12, CCl2F2+e→Cl−+CClF2. The fact that EA of Cl, 3.615 eV is higher than EA of F, 3.399 eV and bond energy of C—Cl, 94.3-95.7 kcal/mole, is weaker than that of C—F 132 kcal/mole explains the dissociation capture of Cl atom of Chlorine contained Freon gases but not for fluorine. Similarly compounds contained Bromine and Iodine will undergo dissociated electron capture to form Br− and I− respectively. An additional data, in the Positive ion mode, quasi-molecular ion of IMS spectra can be collected for identification.
Charge transfer reaction. When bone dry air is used as a carrier and drift gas in IMS, (H2O)nO2− is formed along with lesser intensity of CO4−, CO3−, NO2−, Cl−, and OH−. Under these conditions if sample molecules composed with higher EA such as Cl, Br, I, and F are introduced, the negative charge will be transferred to form Cl−, Br−, I− based on the EA scale.
Proton Abstraction. Because of higher propton affinities of the reactant ions of (H2O)nO2−, CO4−, CO3−, OH−, and NO3−, these reactant ions abstract proton from the unsaturated hydrocarbons which has electron withdrawing functional group such as caryophyllens.
negative ion attachment. This is typically accomplished with the reactant ions of (H2O)nO2−, CO4−, CO3−, OH−, and (H2O)nCl−. For instance, Cl− is added to the site of bivalent atom such as sulfur like mustard gas.